1. Field of the Invention
The present invention relates to a sheet size detection apparatus for detecting the size of a sheet and an image forming apparatus, such as a copying machine, a facsimile machine, a printer or a multifunction machine serving as a combination of those machines, for forming an image on a sheet based on sheet size information obtained by the sheet size detection apparatus.
2. Description of the Related Art
Generally, an image forming apparatus forms an image on a sheet in accordance with the sheet size, and therefore the apparatus main body is designed to recognize the size of a sheet(s) that is set in a sheet feed tray by a user. Some high grade image forming apparatus with which restriction on cost is light are provided with a mechanism that is interlocked with the position of a regulation member for regulating the width direction or the length direction of the sheets on a sheet feed tray to detect the sheet size automatically. However, such a mechanism requires a complex link mechanism or the like, which sometimes causes an increase in the cost. On this account, some common image forming apparatus is provided with a sheet size selection member with which the sheet size setting is selected-by a user manually.
Conventional common sheet size detection apparatus are shown in FIGS. 12 and 13. FIG. 12 is a perspective view showing a sheet feed tray 130 provided with a conventional sheet size detection apparatus 102 using a slide type sheet size selection member 151.
The sheet size selection member 151 is provided on a front edge portion 130e of the sheet feed tray and adapted to be slidable in the direction along the front edge portion 130e shown by the arrow A (i.e. in the horizontal direction). On the backside wall of the sheet size selection member 151, there is provided a predetermined pattern including projections and depressions (not shown).
The sheet size detection apparatus 102 is constructed in such a way that upon setting sheets on the sheet feed tray 130, the user would cause the sheet size selection member 151 to slide in the directions indicated by the double-headed arrow A to a position corresponding to the size of the set sheets to set the size. This is done by adjusting a size pointer 152 of the sheet size selection member 151 with an appropriate position on a sheet size scale provided on the front edge portion 130e of the sheet feed tray 130.
When the user pushes the sheet feed tray 130 in the sheet feeding cassette attaching (or loading) direction indicated by the arrow X to bring it into the main body 101 of the image forming apparatus 100, the sheet size detection apparatus 102 reads the pattern on the sheet size selection member 151 by means of a size detection sensor 150 provided on the apparatus main body 101 to detect the sheet size so that the apparatus main body would recognize the sheet size.
FIG. 13 is a perspective view showing a sheet feed tray 230 provided with a conventional sheet size detection apparatus 202 using a rotary type sheet size selection member 261.
The sheet size selection member 261 is provided on a front edge portion 230e of the sheet feed tray 230 and adapted to be rotatable. On the cylinder side wall 261b of the sheet size selection member 261, there is provided a predetermined pattern including projections and depressions in a manner similar to the above-described slide type sheet size selection member 161.
The sheet size detection apparatus 202 is constructed in such a way that upon setting sheets on the sheet feed tray 230, the user would rotate the sheet size selection member 261 in the direction indicated by the arrow B to cause a sheet size name selected from a sheet size scale provided on the top surface of the sheet size selection member 261 to be aligned with the position of a size pointer 264. When the user pushes the sheet feed tray 230 in the sheet feeding cassette attaching direction indicated by the arrow X to bring it into the main body 201 of the image forming apparatus 200, the sheet size detection apparatus 202 reads the pattern on the sheet size selection member 261 by a size detection sensor 260 provided on the apparatus main body 201 to detect the sheet size so that the apparatus main body would recognize the sheet size.
The conventional sheet size detection apparatus 102 and 202 provided with the sheet size selection member 151 and 261 having the above-described structures have advantages that setting of the sheet size can be performed with a simple structure. However, they suffer from the following problems.
Set positions of the sheet size selection member 151 and 261 are easy to be displaced inadvertently. From the standpoint of improving operability, it is preferable to provide the sheet size selection member 151 or 261 on the front edge portion 130e or 230e of the sheet feed tray 130 or 230. However, with that layout, when the user sets sheets on the sheet feed tray 130 or 230, it is likely that the user""s hands or the sheets touch the sheet size selection member 151 or 261. Consequently, the set position of the sheet size selection member 151 or 261 is sometimes changed upon setting of the sheets, so that the size detection sensor detects a different sheet size.
Furthermore, the image forming apparatus provided with such a sheet size detection apparatus sometimes recognizes the sheet size erroneously. This may cause malfunction of the apparatus or a jam.
The sheet size selection members 151 and 261 are sometimes set to a position displaced from the position to be set to only a small extent. In that case, it is difficult for the user to find the displacement. In aid of user""s operation for positioning the size selection member, the sheet size selection member is generally designed to generate click feeling at predetermined set positions as the sheet size selection member is moved. However, it is not so easy for the user to set the sheet size selection member 151 or 261 to a predetermined position based only on the click feeling.
As per the above, even if the user believes that he or she has set the sheet size correctly, the sheet size may be erroneously set in reality. Furthermore, in the case that the position of the sheet size selection member 151 or 261 is displaced only to a small extent, it is difficult for the user to recognize it visually. Consequently, when the image forming apparatus is in trouble, it will require significant labor and take significant time to find the cause of the trouble.
An object of the present invention is to provide a sheet size detection apparatus that can prevent inadvertent operation mistakes upon sheet loading, enhance visibility and prevent it from being neglected to be operated.
Another object of the present invention is to provide an image forming apparatus equipped with the above-mentioned sheet size detection apparatus with which the possibility of an operation mistake or a sheet jam is low.
A sheet size detection apparatus according to the present invention comprises:
sheet stacking means on which sheets are stacked and which can be loaded into and unloaded from a loading portion;
a sheet size selection member provided on the sheet stacking means, a position of the sheet size selection member being changeable in accordance with a size of stacked sheets;
sheet size detection means provided on the loading portion to detect the sheet size based on a relative positional relationship with the sheet size selection member;
locking means that can lock the sheet size selection member; and
unlock means for releasing a locking operation of the locking means.
Furthermore, a sheet size detection apparatus according to the present invention comprises:
a sheet feed tray detachably provided on an apparatus main body and having an inner plate on which sheets are to be stacked;
a sheet size selector slidably provided on the sheet feed tray and to be set at a position corresponding to a size of the sheets by adjusting a size pointer to a sheet size scale on the apparatus main body;
a size detection sensor provided on the apparatus main body and having a plurality of switches that are to be turned on/off by a portion including projections and depressions provided on the sheet size selector when the sheet feed tray is attached to the apparatus main body;
a plurality of recessed portions formed on the sheet feed tray;
a projection formed on the sheet size selector and adapted to engage with either one of the plurality of recessed portions; and
an unlock lever including the projection on the sheet size selector, the unlock lever being capable of moving the projection away from the recessed portions formed on the sheet feed tray.